U.S. Pat. No. 4,304,744 (assigned to W. R. Grace) is directed to a closure assembly using a polypropylene closure cap. The patent discloses a method of lining the polypropylene closure with a polyvinyl chloride plastisol compound that is fused by microwave techniques. The patent discloses the use of phthalate plasticizers such as diisooctyl phthalate (Example 1) or butyl benzyl phthalate (col. 10, line 47). The main thrust of the patent is the microwave fusing of the lining which requires a preheating step for a good fused lining. The preheat temperature must be at least about 103.degree. C. up to about 160.degree. C. The closure assembly is made without damage to the polypropylene closure.
It is desirable to have a plastisol composition that can be easily used for a lining and effectively fused, without preheating, at a temperature below 130.degree. C., say about 290.degree. F. up to about 300.degree. F., and without the need for microwave energy. The plastisol composition should also be stable with a shelf life of at least about 4 to 6 months.